Light-emitting elements such as a light-emitting diode (hereinafter, referred to as a “LED”) and a semiconductor laser are used in various kinds of light-emitting devices. Among them, the LED may replace an existing light source that uses discharge and radiation, due to the recently increased luminous flux, as well as the smaller size and higher efficiency compared with those of the existing light source. Furthermore, the LED is smaller in size compared with the light source using discharge and radiation, so that the LED has advantages in the applicability to increased applications, the ease of handling, the expectation of various designs, and the like. Thus, the LED is a light source having increased added values.
Furthermore, the LED is capable of controlling the radiation pattern of emitted light, in combination with an optical system having a reflection function and a lens function. Furthermore, if a LED chip measuring several mm per side is used, the chip can be considered as a small point light source, so that the optical system also can be miniaturized.
The radiation pattern from an LED chip mounted on a flat plane generally exhibits a wide-angle radiation pattern called Lambertian that is substantially symmetrical with respect to an optical axis. In order to control a radiation pattern, a reflection member having a reflection function may be placed on the periphery of the LED chip, and a convex lens having a lens function may be placed above the LED chip (see JP 2004-104077 A). Alternatively, examples of controlling a radiation pattern with a diffraction grating (see JP 2005-19987 A) and controlling a radiation pattern with a shielding member covering a part of the LED chip (see JP 2005-5193 A) also are proposed.
However, in the example disclosed by JP 2004-104077 A, due to the use of a convex lens, the miniaturization and reduction in thickness of a light-emitting device may be difficult. Furthermore, in the example disclosed by JP 2005-19987 A, due to the use of a diffraction phenomenon, high-order diffracted light other than 1st-order diffracted light is not used, so that the light output efficiency of the light-emitting device may decrease. Furthermore, in the example disclosed by JP 2005-5193 A, since a part of light emitted from an LED chip is blocked with a shielding member, the light output efficiency of a light-emitting device may decrease.